The purpose of this study is to examine energy balance in Black and White females in late adolescence. The study has two major objectives: 1) To assess energy expenditure and its determinants by estimating energy expenditure of activity (EEA) using the doubly labelled water method (DLW) and measuring resting metabolic rate (RMR); and 2) To asses the validity and reliability of self-reported information on caloric intake and physical activity comparing self reports with information obtained with the DLW procedure. The study will test the hypotheses that Black women have a lower RMR after adjusting for body composition than white women and that lower EEA is associated with obesity. The investigators will also assess different methods of determining body composition by comparing information obtained using total body water (TBW), dual energy x-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), and skinfold measures. A total of 120 women, aged 18-19 years, 60 Black and 60 White, will be randomly selected from subjects currently participating in the multi center NHLBI Growth and Health Study (NGHS). The investigators will obtain data from subjects enrolled at the Cincinnati, Ohio study site. Unique features of the study include a large biracial sample of participants enrolled for the past 10 years in a longitudinal study, and the availability of an extensive database containing lifestyle and behavioral data. The investigators describe analytic procedures for hypothesis testing in detail.